1. Field of the Invention
The present invention relates generally to systems and methods for treating sleep disorders. More particularly, the invention relates to systems and methods for treating obstructive sleep apnea using an adaptive control system for applying air pressure to the nasal airway.
2. State of the Art
Obstructive sleep apnea (OSA) is a newly recognized disease that victimizes 15% of adult males. The disorder arises during sleep when the victim undergoes repeated cessation of breathing. This cessation results from an obstruction of the throat air passage (pharynx) due to a collapse of the throat air passage. Repeated cessation of breathing reduces blood oxygen and disturbs sleep. Reduction in blood oxygen can cause heart attacks and strokes. Sleep disturbances can produce excessive daytime sleepiness, a leading cause of auto accidents.
Medical research over the past decade has provided only one effective and practical approach to OSA therapy, known as nasal continuous positive airway pressure (CPAP). In this therapeutic approach, a patient""s nose is covered with a mask that forms a pressure seal with the surrounding face. While the patient sleeps, the mask is pressurized to a level that distends the collapsible throat air passage, thereby preventing obstruction.
This therapeutic approach provides two significant advantages: it is uniformly effective and it is entirely benign. A major disadvantage of this approach is that the patient must remain overnight in a hospital sleep center to undergo a full night polysomnography study with the pressure mask in place to determine the therapeutic level of pressure. A further disadvantage of this approach is that the pressure delivered to the patient during the polysomnography study is constant and fixed at the prescribed level, even though the patient""s requirements may vary throughout the night and from night-to-night.
The overnight study represents a major bottleneck to treating hundreds of thousands of patients with OSA because it typically requires two full night polysomnographic studies for each new patient: one to establish the diagnosis (diagnostic-polysomnogram) and another to establish the aforementioned therapeutically optimal pressure (therapeutic-polysomnogram). The therapeutic polysmnographic study is necessary to determine the minimum level of pressure required to produce a patent pharyngeal airway (i.e., to determine the necessary therapeutic pressure required for properly treating the patient). These studies, performed in a specialized hospital sleep center, allow a specialist to specify the pressure to be used when prescribing nasal CPAP therapy. For this reason, the therapy cannot be prescribed by an internist or general practitioner.
Due to the requirement of two night polysomnographic studies, hospital sleep centers are crowded even though only a small percentage of OSA victims are presently being treated. Further, the significant cost of the overnight polysomnographic study by a hospital sleep center represents a significant obstacle to diagnosing and treating the large population of sleep apneics. The backlog of undiagnosed and untreated OSA patients thus represents a substantial public health problem.
To address the foregoing drawbacks of existing approaches to diagnosis and treatment of OSA, recent commercial technology provides overnight, unattended monitoring of breathing in the patient""s home. Such unattended monitoring generally permits the physician to diagnose OSA without requiring a diagnostic overnight study in the hospital sleep center. However, a hospital sleep center is still required for establishing the therapeutically optimal pressure of nasal CPAP in each patient. Accordingly, medical practitioners have been slow to use the new monitoring technology for diagnostic purposes since the patient must, in any case, be referred to a sleep center for a full night therapeutic polysomnographic study.
Accordingly, it would be desirable to render the diagnosis and therapy of OSA more practical, convenient and inexpensive. To achieve this end, a method and system for automatically establishing the desired nasal CPAP pressure is needed. More particularly, a positive airway pressure system is required which will allow a physician, following diagnosis with convenient monitoring technology, to prescribe nasal CPAP without specifying the pressure.
The present invention is therefore directed at providing a practical, convenient and cost-effective system for diagnosing and treating OSA. Further, the invention is directed to portable systems and methods for automatically and continuously regulating the level of nasal pressure to an optimal value during OSA treatment. OSA therapy is implemented by automatically applying an appropriate pressure level to a patient. The applied pressure is continuously re-evaluated and optimized. This optimal level varies with body position and stage of sleep throughout the night. In addition, the required pressure varies depending upon the patient""s body weight and whether or not any deleterious substances, such as alcohol or sleeping medicine, have been ingested.
Thus, the present invention relates to systems and methods for adaptively providing continuous positive airway pressure to an upper airway system by detecting airflow data in the upper airway system at predetermined increments of time; averaging said airflow data over a second period of time which includes a plurality of said predetermined time increments; determining non-respiratory airflow using said averaged data; identifying periods of inspiration and expiration using said non-respiratory airflow data; extracting information or features from said airflow data; and continuously adjusting pressure in said upper airway system.
In a preferred embodiment, a portable adaptive control system is provided which continually searches for the optimal minimum pressure required to adequately distend a patient""s nasal pharyngeal airway. By rendering the system portable, a large percentage of OSA victims can be cost-effectively treated in their homes, thus reducing the overcrowding in expensive hospital sleep centers. Optimal minimum pressure is used because higher pressures increase the likelihood of side effects (e.g., daytime rhinitis), and reduce the likelihood of patient compliance. A patient""s compliance in regularly using the system is a significant concern inasmuch as the system is a portable device used at the patient""s home without the supervision of a hospital sleep center specialist.
To address the need for a practical device which will further enhance patient compliance, transducers must not be placed on or in the patient""s body. Rather, all information used for automatic pressure adjustments is derived by continuously measuring airflow from the pressure generating source (blower) to the nasal mask. Airflow is measured quantitatively by a pneumotachograph interposed between the pressure generating source and the mask. This continuous measure of airflow provides a feedback signal for the adaptive control system to maintain a desired level of output pressure.